Genomic inference of contemporary effective population size in a large island population of collared flycatchers (Ficedula albicollis).

Due to its central importance to many aspects of evolutionary biology and population genetics, the long-term effective population size (Ne ) has been estimated for numerous species and populations. However, estimating contemporary Ne is difficult and in practice this parameter is often unknown. In principle, contemporary Ne can be estimated using either analyses of temporal changes in allele frequencies, or the extent of linkage disequilibrium (LD) between unlinked markers. We applied these approaches to estimate contemporary Ne of a relatively recently founded island population of collared flycatchers (Ficedula albicollis). We sequenced the genomes of 85 birds sampled in 1993 and 2015, and applied several temporal methods to estimate Ne at a few thousand (4000-7000). The approach based on LD provided higher estimates of Ne (20,000-32,000) and was associated with high variance, often resulting in infinite Ne . We conclude that whole-genome sequencing data offers new possibilities to estimate high (>1000) contemporary Ne , but also note that such estimates remain challenging, in particular for LD-based methods for contemporary Ne estimation.